Related Rates - Angle rate

I'm not sure weather this is correct or not, but I gave it my best shot and it looks correct... but I'm not sure if it is.

A 10 ft plank is leaning against a wall. If at a certain instant the bottom of the plank is 2 ft from the wall and is pushed toward the wall at a rate of 6 in/sec, how fast is the acute angle that the plank makes with ground increasing?